Ring rolling mill

ABSTRACT

A ring rolling mill effects an increase in the diameter of ringshaped workpieces by reduction in the distance between working rolls operating on opposite peripheries of the ring to decrease its radial thickness, with at least one working roll being driven, and includes at least one ring-engaging cnetering roll displaced in accordance with the increase in the ring diameter. At least one feeler engages a periphery of the ring and measures the ring diameter, and is connected to control effecting displacement of the centering rolls in accordance with the measured ring diameter. The centering rolls are rotatably mounted on pivoted levers, and the control includes a final control element for pivoting each lever. The control may include hydraulic, mechanical or electrical control elements, and the feelers may be incorporated with the centering rolls.

United States Patent [1 1 Jeuken et al.

[451 Jan. 14,1975

RING ROLLING MILL Inventors: Josef Jeuken, Holzwickede; Gustav Vieregge, Dortmund-Wambel; Wolfgang Massberg, Dortmu ND-Wellinghofen, all of Germany Assignee: Rheinstahl AG, Essen, Germany Filed; May 7, 1973 Appl. No.: 357,777

Foreign Application Priority Data May 9, 1972 Germany 2222607 U.S. Cl. 72/10, 72/110 Int. Cl B21h 1/06 Field of Search 72/105, 106, 107, 110,

References Cited UNITED STATES PATENTS Cowles et al. 72/107 Wieting 72/10 Wieting et al. 1. 72/10 [57] ABSTRACT A ring rolling mill effects an increase in the diameter of ring-shaped workpieces by reduction in the distance between working rolls operating on opposite peripheries of the ring to decrease its radial thickness, with at least one working roll being driven, and includes at least one ring-engaging cnetering roll displaced in accordance with the increase in the ring diameter. At least one feeler engages a periphery of the ring and measures the ring diameter, and is connected to control effecting displacement of the centering rolls in accordance with the measured ring diameter. The centering rolls are rotatably mounted on pivoted levers, and the control includes a final control element for pivoting each lever. The control may include hydraulic, mechanical or electrical control elements, and the feelers may be incorporated with the centering rolls.

14 Claims, 6 Drawing [Figures PATENTEI] JAN 4 I975 SHEEI 10F 5 PATENTED JAN 1 41975 SHEET 3 UF 5 PATENTEU JAN 1 41975 sum s of s RING ROLLING MILL FIELD AND BACKGROUND OF THE INVENTION This invention is directed to a ring rolling mill wherein the increase of the diameter of ring-shaped workpieces is effected by reducing the distance between at least two working rolls acting on opposite peripheries of the ring with at least one working roll being driven, the mill including at least one centering roll engaging a periphery of the ring and displaced in accordance with the increase in the ring diameter.

Ring rolling mills of the type to which the present invention is directed usually are provided with two centering rolls arranged symmetrically with respect to the common plane of the working roll axes, and which are pressed into contact with the outer periphery of the ring being worked. The centering rolls are provided to prevent lateral migration of the ring during the rolling process and to attain, as far as possible, an accurate circular form of the ring. The pressure or bias on the centering rolls must be so adapted to the varying adjusting force resulting from the change in diameter of the ring that, on the one hand, the ring is not deformed by the centering rolls and, on the other hand, the ring does not flutter or perform other uncontrolled translatory oscillations because of insufficient bias or pressure on the centering rolls. These centering rolls are usually mounted in pivoted levers pivotal about pivots fixed on the rolling mill frame. Due to the increasing ring diameter during working thereof, the displacement of the centering rolls occurs on paths determined by the arrangement of the pivoted levers.

It has been found extremely difficult in practice, and it requires constant attention on the part of operators, to constantly adapt the pressure of the centering roll optimally to the rigidity or adjusting force exerted by the ring and which decreases with increasing reduction of the radial thickness of the ring. In particular when rolling thinner rings, there is an increased risk that the ring will push to the outside between the rolling zone and the centering roll, and form a loop so that the ring becomes unusable.

' It has already been tried to eliminate the above mentioned inconveniences by mounting the roll mandrel in a table turning eccentrically about the main roll, and by producing the pressure exerted by the centering rolls through the medium of a cam disc. In this known embodiment of a ring rolling mill with centering rolls, the operator must also adapt the selection and the adjustment of the cam disc to the anticipated varying rigidity of the ring, so that it depends on the skill of the operator whether fluttering of the ring and ring deformations can be positively prevented.

SUMMARY OF THE INVENTION The invention is directed to the problem of providing a ring rolling mill, of the above-mentioned type with at least one centering roll and preferably with two centering rolls, in such a way that the displacement of the centering rolls, caused by the increase in the diameter of the ring, is not effected by the adjusting force of the expanding ring or requires only a weak adjusting force, and that the problematic adaptation of the pressure of the centering rolls and of the adjusting force of the ring is eliminated or at least takes place in a region where it can be better controlled than heretofore, and where it is independent of the skill and attention of the operator.

For this purpose, the invention comprises one or more feelers determining the ring diameter and effecting, through a guidance control, a displacement of at least one or of all the centering rolls. The guidance control preferably comprises respective measuring transformers associated with each feeler, an intensifier and at least one final control element for the centering rolls, so that the command variables derived from the measuring transformers determine clearly the value of the manipulated variable of each final control element, during the rolling process.

The feelers determining the ring diameter can be designed as contact-free elements or as wing contact elements, for example, in the form of a feeler roll whose contact pressure is low compared to the risk of ring deformation. The solution to the problem, as provided in accordance with the invention, is based on the finding that the disadvantages of the known embodiments are due to the linkage of cause and effect, because the adjusting force exerted by the ring effects, at the same time, the position of the centering rolls, and the latter, in turn, effect the guidance of the ring. The invention eliminates this cause-effect linkage, with the above mentioned advantageous results.

The feeler or feelers for determining the instantaneous ring diameter, increasing with the advance of the working rolls toward each other, can be arranged at different points relative to the ring. In the simplest form, the measuring feeler is arranged in the common plane of the axes of the two working rollls acting on the ring.

In those ring rolling mills where a deviation of the ring from the exact circular form must be expected at least sometimes, particularly in ring rolling mills with more than one pair of working rolls, several feelers preferably are used and are arranged outside the plane defined by the axes of the working rolls acting on the ring, for example, in the form of at least two feeler rolls arranged on the outer periphery of the ring and preferably diametrically opposite each other.

In ring rolling mills with several centering rolls, it is known to couple the centering rolls mechanically or hydraulically with each other so that the position of one centering roll determines, at the same time, the position of all the other centering rolls. In this case, a final control element receiving the signal from the measuring intensifier preferably is assigned to a first centering roll which, due to the coupling, effects simultaneously the displacement of the other centering rolls. However, instead of the coupling of the centering rolls, each centering roll can also be provided with a respective final control element receiving a signal from the measuring intensifier, and this is particularly advisable in the case of ring rolling mills for large ring diameters, or if different adjusting paths for the individual centering rolls are required for the introduction and removal of the workpiece from the side of the mill.

In a preferred embodiment of the invention, each centering roll has at least one yielding abutment arranged between the final control element and the centering roll, which permits a limited deviation from the nominal value of the centering roll bearings. In cooperation with the guidance control of the centering rolls, which determines their position in dependence on the instantaneous ring diameter, with such an abutment it can be attained that the ring is guided reliably by the rolls during the entire rolling process, and that the risk of a ring deformation or of dangerous ring fluttering is avoided The characteristic of the abutment, which can consist, for example, of a mechanical spring and of a hydraulic damping element acting thereafter, can be so formed that the ring is guided gently in a nominal position and is stabilized again in the centered position with an uncritical restoring force, when the position starts to change.

This embodiment of the ring rolling mill in accordance with the invention makes it possible to design the ring rolling mill particularly in such a way that the relation between ring diameter and associated positions of the centering rolls can be varied by a correcting element inluencing the output variable of the measuring intensifier, preferably according to a fixed program. The program-controlled correcting element permits guidance of the ring by the centering rolls in such a way that the guidance follows optimally the changing conditions.

Ring rolling mills usually have two centering rolls which are arranged symmetrically to the common plane through the axes of the working rolls acting on the ring. On each of the two centering rolls, there can be arranged a feeler which determines a deviation from the nominal value of the position determined by the guidance control, and which restores the nominal value of the centering roll position through corresponding control means.

Known ring rolling mills frequently are equipped with two working rolls acting radially on the ring and two rolls acting axially on the ring, with at least one roll of each roll arrangement being driven. In these ring rolling mills, the mutual adaptation of the drive is not easy, and there is particularly a risk that the known centering roll guidance will fail and the ring to be rolled will be subjected to the above mentioned adverse influences and become unusable. Accordingly, the invention is applicable with particular advantage to these ring rolling mills. In accordance with the invention, such a ring roll ing mill can be so designed that the measured values of the feelers, which determine the deviations, from the nominal value, of the positions of the two centering rolls as determined by the guidance control, are compared with each other in a measuring bridge, and that a mistuning of the bridge causes an unsymmetrical change on an abutment, counteracting the displacement of the centering rolls. This can also be a hydraulic system with an adjustable throttle.

Another feature, when added to the preceding features of the invention, provides that the nominal position of the centering rolls determined by the final control element of the guidance control can be restored by means of a control device for varying the relation between the speed of the driven rolls. In a ring rolling mill which has centering rolls whose position can be changed directly by the increase of the ring diameter against the action of a mechanical, hydraulic, or other force, the invention also can be used with advantage by utilizing an additional guidance control for the direct displacement of the centering rolls through one or several feelers and final control elements, and which can be connected additionally during selected partial rolling periods or which can act alone.

Finally, the invention provides, for a ring rolling mill with at least two centering rolls, a feeler assigned to each centering roll and supported with limited yield relative to its final control element, with the intensifier influencing the final control element or control elements for the centering rolls in the sense of an equal displacement of all centering rolls corresponding to the increase of the ring diameter, but only if all the feelers are affected equally. In this way, a proper centering of the ring can be attained with little technical expenditures, and without the risk of a deformation of the ring. This is made possible by the fact that, when the ring is displaced from the desired central position, which results in a corresponding irregular deflection of the centering rolls and thus of the feelers, the displacement of the centering rolls is delayed or preferably completely eliminated until the ring again assumes the centered position and thus acts uniformly on all the centering rolls and feelers.

An object of the invention is to provide an improved ring rolling mill.

Another object of the invention is to provide such a ring rolling mill including feelers detecting and measuring the ring diameter during rolling of the ring.

A further object of the invention is to provide such a ring rolling mill in which the disadvantages of prior art ring rolling mills are obviated.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a diagrammatic elevational view of a ring rolling mill embodying the invention, with a pair of radial working rolls and a centering roll;

FIG. 2 is a similar view illustrating the ring rolling mill with two centering rolls;

FIG. 3 is a diagrammatic elevational view of a ring rolling mill with a pair of radial working rolls and a pair of rolls engaging opposite axial end surfaces of the ring;

FIG. 4 is a view similar to FIG. 3 but illustrating a different embodiment of the centering roll control.

FIG. 5 is an elevation view illustrating the mechanical constructional design of a ring rolling mill in accordance with the invention, with the control means being omitted; and

FIG. 6 is a diagrammatic elevational view of another embodiment of a ring rolling mill in accordance with the invention and having two centering rolls.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, in the embodiment of the invention therein illustrated, the increase in the diameter of a ring 1, constituting a ring-shaped workpiece, is effected by a reduction of the distance between the two working rolls 2 and 3, namely the driven disc roll 2 rotatably mounted in a fixed position in the rolling mill frame, which has not been shown, and of the undriven roll mandrel 3 which is adjustable with respect to the driven disc roll 2. A centering roll 4 has the function of guiding ring 1, and can be swung, through a pivoted lever 5, about a pivot 6 fixedly mounted in the rolling mill frame.

In accordance with the invention, in the common plane of the axes of the two working rolls 2 and 3, a feeler 7, bearing as a feeler roll on the outer circumference of ring 1, determines or measures the diameter of ring 1. The deflection of feeler 7 is the input variable for the guidance control of the centering roll. This guidance control comprises a measuring transformer 8, a measuring intensifier 9 and a final control element 10, which latter acts on pivoted lever 5 and thus brings centering roll 4 into a position corresponding to the instantaneous ring diameter. An actual value-nominal value comparison is possible by a measuring instrument 11, comprising a feeler and a measuring transformer, and which is connected over return line 12 to intensifier 9, so that the actual value can be correspondingly corrected.

In the ring rolling mill shown in FIG. 2, ring 1 is guided by two centering rolls 4 whose respective pivoted levers 5 are adjusted by associated final control elements in accordance with the increase in the ring diameter. By means of a correcting element 13, the manipulated variable of the final control elements 10, associated with a certain deflection of feeler 7, and thus the position of centering rolls 4 can be varied arbitrarily or according to a fixed program. Between each final control element 10 and the associated centering roll 4 there is arranged a yielding abutment 14 in the form of a compression spring and which permits a limited deviation of the position of the centering roll from a nominal value. The contact pressure of centering rolls 4 on the outer periphery of ring 1 can be adapted optimally and in timed dependence on the rigidity of ring 1, and thus other variables of state, by the cooperation of the program-controlled correcting element 13 and the yielding abutment 14. When ring 1 migrates to one side, for example upwardly as viewed in FIG. 2, the spring 14 on upper centering roll 4 generates a braking and restoring force which prevents fluttering of the ring and which effects the return of the ring into its normal position.

In the ring rolling mill shown in FIG. 3, there are, in addition to the two radial working rolls 2 and 3, two conical rolls 15 which act axially on ring 1, the contact roll 15 shown in FIG. 3 being driven. The speeds of the respective drives of disc roll 2 and conical roll 15 can be so attuned to each other by means of speed governor 16 that the track speeds of ring 1 are identical at the two roll gaps during the entire rolling process. Both pairs of rolls are mounted for displacement in the rolling mill frame. They are so moved outwardly with increasing ring diameter that the center axis of ring 1 re mains stationary. Two feelers 7 arranged on the outer periphery of ring 1 symmetrically to the common plane of the axes of rolls 2 and 3 determine the increasing radius of the ring. Their deflection controls the displacement of the two pairs of rolls 2, 3 and 15, 15, of which the second roll 15 is not specifically illustrated. Two centering rolls 4 are alo arranged symmetrically to the common axial plane of the working rolls 2 and 3, and the pivots 6 of their respective levers 5 are mounted on the carriage (not shown) which also carries the pair of working rolls 2 and 3 and makes them displaceable toward the rolling mill frame.

The two feelers 7, determining the instantaneous ring radius or diameter, supply, through their respective measuring transformers 8, the input to intensifier 9 with the correcting element 13, which causes, in the final control element 10, the manipulated relative to set the position of centering rolls 14 in dependence on the radius or diameter of ring I. The lower centering roll 4, as viewed in the drawing, is mechanically coupled with the upper centering roll 4 through a gearing 17.

On centering rolls 4, there are arranged respective feelers 18 with measuring transformers which determine the deviation of the actual position of the associated centering roll from the nominal value, and whose output signals are fed to a control device for restoring the position of the centering rolls determined by final control element 10. In the illustrated example, the control device comprises a measuring bridge 19 whose adjusting motor 20, arranged in the zero branch, influences the speed governor 16 for the drive of the lower conical roll 15, so that the relation between the speeds of driven rolls 2 and 15 is varied.

During the rolling of rings, particularly rings with a flange profile, a displacement of the pitch point occurs, which is difficult to control, with the result that the relations between the speeds of the driven working roll 2 and the track speed varying with the ring thickness is subject to variations. Similar phenomena of the displacement of the pitch point appear also in the roll gap of axial rolls 15. The different track speeds in the two roll gaps causes, in this case, a unilateral migration of the ring, which latter cannot be brought back into the centered position, in most cases, even by a high restoring force of the centering rolls, but which may cause a risk of deformation of the ring.

When ring 1 leaves its centered position in the embodiment of the invention shown in FIG. 3, the measuring feelers 18 are deflected unequally and the measuring bridge 19 is correspondingly mistuned. The adjusting motor 20, in the zero branch of bridge 19, then causes such a change of the speed of the driven axial roll 15 that ring 1 returns into its centered position without the application of external forces. In the conical axial rolls, it is also possible to change the position of these rolls relative to the ring, instead of changing the speed. Measuring rolls 4, with their feelers 18, then reassume a symmetrical position relative to the common plane of the axes of working rolls 2 and 3, and measuring bridge 19 is restored to the balanced state. The above described inconveniences of known fourroll ring rolling mills are therefore positively prevented. The success of the operation does not depend at all on the attention and skill of the operator, but can be attained reliably and readily under all customary conditrons.

The ring rollingrmill shown in FIG. 4 has the feature that the deflection of the feeler 7, caused by the increase of the ring diameter, controls final control ele ments 21 which are designed, at. the same time, as yielding controllable abutments. If the ring diameter increases during rolling in the centered position, the two centering rolls 4 undergo, by the manipulated variables in final control elements 21, caused by the deflection of feeler 7, a displacement corresponding to the guidance control, with the springs 14, as yielding abutments, causing, as mentioned above, an adapted pressure of the associated centering roll 4 through correcting element 13 of intensifier 9. If the ring migrates to one side, upwardly, for example, as viewed in FIG. 4, the additional spring force can be reduced by corresponding opening of the associated throttle 22 in such a way that it is controlled by the mistuning of measuring bridge 19 caused by upper feeler 18. In this way, a deformation of the ring can be positively prevented even in less rigid rings.

In the meantime, the mistuning of bridge 19 has caused an additional speed correction of the driven conical roll 15, so that ring 1 returns into the center postion. Throttle 22, which has closed in the meantime, permits final control element 21 to return the centering roll 4 into its normal position. An essential advantage is seen in the fact that the yielding abutment of the centering rolls 4 comprises two structural elements whose line of force is variable and thus can be adapted optimally to the respective rolling conditions. The feared fluttering of the rings, the danger of loop formation, and deformation of the rings, which makes them unusable, are thus positively prevented.

FIG. illustrates the mechanical construction of the ring rolling mill diagramatically illustrated in FIG. 4, with the control means, embodying the invention, for guiding the rolling mill and the ring to be rolled being omitted for the sake of clarity. The rolling mill comprises the horizontal rolling stand 23 and the vertical edging stand 24. In the rolling mill frame 25 common to the two stands, there is fixedly mounted the kingpin 26, with the disc roll 2, and which is driven by a transmission 27 from an electric motor 28. Opposite disc roll 2, and displaceable relative thereto, there is mounted, in a hydraulically adjustable carriage 29, the undriven roll mandrel 3. Roll mandrel 3 is supported, at its upper end, by the vertically displaceable frametype arm brackets 30. The two centering rolls 4 can be turned through their pivoted levers 5 about the pivot 6, so that the centering rolls can be adjusted relative to the ring to be rolled, and which has not been shown.

Edging stand 24 is mounted on rolling mill frame 25 for horizontal displacement in slideways, and the displacement is effected by means of the double acting hydraulic cylinder 31. In the lower part of edging stand 24, there is fixedly mounted the lower conical roll which is driven, through a fixed transmission 32, by an electric motor 33. The transmission and the motor are so designed that the speed of the lower conical roll 15 can be so regulated that the circumferential speed of this conical roll can be varied infinitely over the entire length of its conical shell, to correspond to the rolling speed of disc roll 2. Upper conical roll 15 is mounted for free rotation in a carriage 34 which can be adjusted in the axial direction of the ring to be rolled through a worm gear 36 driven by a motor 35 and a spindle drive 37. In addition, carriage 34 can be lowered hydraulically, which has not been illustrated, to exert a vertical rolling force in the axial direction of the ring to be rolled. Between the two conical rolls 15, there is arranged a feeler in the form of a feeler roll 7.

The ring rolling mills shown in FIGS. 1, 2 and 3, and in FIG. 6, are designed, in their mechanical construction, generally in the same way, with differences in certain parts as mentioned above. For example, the vertical edging stand is naturally eliminated if the ring rolling mill does not have vertical rolls.

FIG. 6 illustrates a ring rolling mill having two centering rolls 4 which are yieldingly supported, through compression springs 14, on pivoted levers 5 pivotal about stationary pivots 6 mounted in the rolling mill frame which has not been shown in FIG. 6. Pivoted levers 5 are coupled with each other through a gearing 17 so that their movement is symmetrical. On upper pivoted lever 6, as viewed in FIG. 6, there acts a final control element 10 comprising a piston articulated to pivoted lever 5 and a hydraulic cylinder secured on the rolling mill frame. There is connected to the cylinder chamber, from which hydraulic fluid is displaced when pivoted levers 5 move apart, an intensifier 9 in the form of a magnetic valve which opens freely or through a throttle into a tank 38. On pivoted levers 5, there are arranged feelers 18 in the form of limit switches which move through a certain distance under the action of compression springs 14 when centering rolls 4 are displaced relative to pivoted levers 5. Feelers 18 are so connected with intensifier 9 that the intensifier opens the above-mentioned outlet from final control element 10 only when both feelers respond, but otherwise keeps the outlet closed.

The arrangement of FIG. 6 operates in a manner which will now be described. When ring 1 increases its diameter during the rolling process and remains centered in its normal position, the two centering rolls 4 are displaced relative to pivoted levers 5, compressing compression springs 14 through a certain distance, and both feelers 18 respond by actuating the limit switches. Intensifier 9 thus permits the outflow of the hydraulic fluid displaced by the piston of the final control element l0, and the pivoted levers open in correspondence to the increase in the ring diameter. Since ring 1 has to transmit to centering rolls 4 only the force for compressing springs 14, for displacing the hydraulic fluid and for overcoming the mechanical friction, deformation of the ring, even with a low rigidity thereof, is positively prevented with a corresponding layout.

If the ring leaves its centered position, due to some undesired forces, and migrates upwardly, for example, as viewed in FIG. 6, upper centering roll 4 is displaced further toward upper pivoted lever 5, compressing upper compression spring 14 further, while the lower centering roll moves away from the lower pivoted lever 5 under the action of its compression spring and releases its limit switch. The intensifier 9 thus interrupts the outflow from the cylinder of the final control element, so that the pivoted levers 5 cannot open any further. The further increase of the ring diamter is therefore limited in the upward direction by the upper centering roll, and the ring center must move downward again until the ring has reassumed the center position and the uniform opening movement of both pivoted levers is made possible by actuating again the lower limit switch. This re-centering of the ring likewise stresses the rigidity of the ring to a relatively minor extent, so that a good action is achieved with very little technical expenditure and independent of the skill of the operator.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In a ring rolling machine effecting an increase in the diameter of ring-shaped workpieces by reduction in the distance between two radial working rolls operating on respective opposite peripheries of the workpiece to decrease its radial thickness and the distance between two axial working rolls acting on respective opposite edge surfaces of the workpiece to decrease its axial thickness, with at least one working roll of each pair being driven and with at least one pair of rolls being mounted for displacement in the longitudinal direction of the ring rolling machine, the improvement comprising, in combination, at least one centering roll engageable with the periphery of the workpiece; respective actuating members associated with each centering roll and operable to displace the associated centering roll in accordance with the increasing diameter of the ringshaped workpiece; at least one first feeler detecting the instantaneous diameter of the workpiece and controlling said actuating members; a further actuating member operatively associated with at least one of said rolls; and a further feeler positioned outside the plane including the axes of the two radial working rolls, for detecting an unsymmetrical position of the workpiece relative to said plane, and controlling said further actuating member to effect the return of the workpiece into its symmetrical position relative to said plane.

2. In a ring rolling machine, the improvement claimed in claim 1, in which said first feelers determine the increase of the workpiece diameter by direct contact with the workpiece.

3. In a ring rolling machine, the improvement claimed in claim 1, in which said first feelers determine the workpiece diameter indirectly.

4. In a ring rolling machine, the improvement claimed in claim 1, in which said further actuating member is operatively associated with said working rolls.

5. In a ring rolling machine, the improvement claimed claim 4, in which said further actuating member is operable to change the driving speed of one of said pairs of working rolls to effect return of the ringshaped workpiece into the symmetrical position.

6. -In a ring rolling machine, the improvement claimed in claim 1, in which said further actuating member is operatively associated with at least one centering roll.

7. In a ring rolling machine, the improvement claimed in claim 6, in which, responsive to a migration of the workpiece out of its symmetrical position, saud further actuating member changes the position and contact pressure of said at least one centering roll.

8. In a ring rolling machine, the improvement claimed in claim 1, in which, responsive to a migration of the ring-shaped workpiece out of its symmetrical position, said further actuating member effects an instantaneous simultaneous migration of the associated centering rolls with a small contact pressure and, in addition, changes the driving speed of one of said pairs of working rolls whereby the ring-shaped workpiece returns into its symmetrical position.

9. In a ring rolling machine, the improvement claimed in claim 1, in which there are two centering rolls arranged symmetrically with respect to the common axial plane of said two radial working rolls, and adapted to change their respective positions automatically; each centering roll having a respective feeler mounted thereon for detecting the position of the associated centering roll; comparison signal producing means connected to said feelers and supplying a comparison signal derived from the values measured by said feelers to said further actuating member for returning the ring-shaped workpiece into its symmetrical posi' tion.

10. In a ring rolling machine, the improvement claimed in claim 9, in which said comparison signal producing means comprises a measuring bridge connected to said feelers and producing a comparison signal responsive to electrical unbalance of said measuring bridge.

11. In a ring rolling machine, the improvement claimed in claim 10, including means coupling said two centering rolls to each other; a common actuating member operable to displace both centering rolls in accordance with the increasing diameter of the ringshaped workpiece; and means connecting at least one of said feelers, detecting the instantaneous diameter of the workpiece, with said common actuating member to automatically displace both centering rolls.

12. In a ring rolling machine, the improvement claimed in claim 9, including respective positiondetermining actuating members associated with each of said two centering rolls; said position-determining actuating members comprising hydraulic actuators each controlled by the feeler associated with the respective centering roll; said further actuating member comprising at least one controllable choke additionally influencing the hydraulic actuators.

'13. In a ring rolling machine, the improvement claimed in claim 1, including respective amplifiers, constituting correction members, connected between each first feeler and the associated actuating member; said amplifiers being operable to change the relation between the measured and the respective manipulated variables.

14. In a ring rolling machine, the improvement claimed in claim 13, in which said amplifiers constituting correction members are operable to change the relation between the measured and the manipulated variables in accordance with a predetermined program. 

1. In a ring rolling machine effecting an increase in the diameter of ring-shaped workpieces by reduction in the distance between two radial working rolls operating on respective opposite peripheries of the workpiece to decrease its radial thickness and the distance between two axial working rolls acting on respective opposite edge surfaces of the workpiece to decrease its axial thickness, with at least one working roll of each pair being driven and with at least one pair of rolls being mounted for displacement in the longitudinal direction of the ring rolling machine, the improvement comprising, in combination, at least one centering roll engageable with the periphery of the workpiece; respective actuating members associated with each centering roll and operable to displace the associated centering roll in accordance with the increasing diameter of the ring-shaped workpiece; at least one first feeler detecting the instantaneous diameter of the workpiece and controlling said actuating members; a further actuating member operatively associated with at least one of said rolls; and a further feeler positioned outside the plane including the axes of the two radial working rolls, for detecting an unsymmetrical position of the workpiece relative to said plane, and controlling said further actuating member to effect the return of the workpiece into its symmetrical position relative to said plane.
 2. In a ring rolling machine, the improvement claimed in claim 1, in which said first feelers determine the increase of the workpiece diameter by direct contact with the workpiece.
 3. In a ring rolling machine, the improvement claimed in claim 1, in which said first feelers determine the workpiece diameter indirectly.
 4. In a ring rolling machine, the improvement claimed in claim 1, in which said further actuating member is operatively associated with said working rolls.
 5. In a ring rolling machine, the improvement claimed claim 4, in which said further actuating member is operable to change the driving speed of one of said pairs of working rolls to effect return of the ring-shaped workpiece into the symmetrical position.
 6. In a ring rolling machine, the improvement claimed in claim 1, in which said further actuating member is operatively associated with at least one centering roll.
 7. In a ring rolling machine, the improvement claimed in claim 6, in which, responsive to a migration of the workpiece out of its symmetrical position, saud further actuating member changes the position and contact pressure of said at least one centering roll.
 8. In a ring rolling machine, the improvement claimed in claim 1, in which, responsive to a migration of the ring-shaped workpiece out of its symmetrical position, said further actuating member effects an instantaneous simultaneous migration of the associated centering rolls with a small contact pressure and, in addition, changes the driving speed of one of said pairs of working rolls whereby the ring-shaped workpiece returns into its symmetrical position.
 9. In a ring rolling machine, the improvement claimed in claim 1, in which there are two centering rolls arranged symmetrically with respect to tHe common axial plane of said two radial working rolls, and adapted to change their respective positions automatically; each centering roll having a respective feeler mounted thereon for detecting the position of the associated centering roll; comparison signal producing means connected to said feelers and supplying a comparison signal derived from the values measured by said feelers to said further actuating member for returning the ring-shaped workpiece into its symmetrical position.
 10. In a ring rolling machine, the improvement claimed in claim 9, in which said comparison signal producing means comprises a measuring bridge connected to said feelers and producing a comparison signal responsive to electrical unbalance of said measuring bridge.
 11. In a ring rolling machine, the improvement claimed in claim 10, including means coupling said two centering rolls to each other; a common actuating member operable to displace both centering rolls in accordance with the increasing diameter of the ring-shaped workpiece; and means connecting at least one of said feelers, detecting the instantaneous diameter of the workpiece, with said common actuating member to automatically displace both centering rolls.
 12. In a ring rolling machine, the improvement claimed in claim 9, including respective position-determining actuating members associated with each of said two centering rolls; said position-determining actuating members comprising hydraulic actuators each controlled by the feeler associated with the respective centering roll; said further actuating member comprising at least one controllable choke additionally influencing the hydraulic actuators.
 13. In a ring rolling machine, the improvement claimed in claim 1, including respective amplifiers, constituting correction members, connected between each first feeler and the associated actuating member; said amplifiers being operable to change the relation between the measured and the respective manipulated variables.
 14. In a ring rolling machine, the improvement claimed in claim 13, in which said amplifiers constituting correction members are operable to change the relation between the measured and the manipulated variables in accordance with a predetermined program. 